A close look at existing eigenvalue problems producing characteristic fields [1]} and currents [2]} reveals that these scattering- and impedance-based formulations represent the same physical problem, only using different representations. This raises an important question of whether other representations exist and, if so, whether they have advantageous properties over existing approaches. This paper addresses these questions utilizing a scattering dyadic [3]}, which affords the possibility for characteristic modes to be evaluated in arbitrary numerical methods, to be calculated for objects constructed from arbitrary materials, and to be reconstructed from far-field measured data.
